1. Field of the Invention
This invention relates to ink jet recorded matter having a pigment ink image formed on a porous ink receiving layer, a process for producing the same, and a thermal transfer sheet, an ink jet recording apparatus, a thermal transfer apparatus, and an ink jet recording medium, which can be used in the production process.
2. Description of Related Art
Ink jet recording is an image recording technology in which ink droplets ejected from small nozzles of a recording head are adhered to a recording medium such as paper to form an ink image. Formation of high quality images, comparable to silver salt photographs, by ink jet recording needs large quantities of ink so that recording media used therefor are required to have high ink receptivity. Use of a plurality of ink formulations equal in hue but different in colorant concentration has recently been spreading to form high quality images with reduced graininess in highlights, and the demand for ink receptivity of recording media has been increasing with this trend. To meet the demand, recording media for ink jet recording, which exhibit high ink absorptivity and which are capable of forming high quality full color images comparable to silver salt photographs have been developed. The recording media of this type comprise a substrate, such as paper or a film, having thereon provided a porous ink receiving layer made mainly of ultrafine particles of inorganic pigments, such as colloidal silica, vapor phase deposited silica, alumina hydrate and γ-alumina.
Aqueous inks are generally used in ink jet recording, which are solutions or dispersion of colorants including dyes and pigments in aqueous media such as water and alcohol-containing water. These inks are largely classified into dye inks and pigment inks. Dye inks have been in frequent use for their high color reproducibility, high water solubility and other advantages over pigment inks. However, dye ink images formed on a porous ink receiving layer have poor fastness and are liable to discoloration and fading with time by the influences of water, moisture, ozone gas, etc. Considering that ink jet recorded image fastness has been gaining importance with broadening applications of ink jet recording technology to digital photography and commercial printing, improvement in image fastness has now come to be an important subject in the ink jet recording art. Hence, use of pigment inks which are superior to dye inks in image fastness to light, water, etc. has been increasing.
Nevertheless images formed of pigment inks is disadvantageous in that a pigment, which merely adheres onto the surface of a recording medium, has poor scratch resistance and easily comes off. Images formed of pigment inks have another problem of gloss unevenness between image areas and non-image areas and among image areas with different attached amounts of pigment. Further, pigment images formed on a porous ink receiving layer, while superior in fastness to those formed of dye inks, can undergo discoloration and fading with time due to ozone gas, heat, etc. and are not seen yet as having sufficient fastness for practical use.
In reference to protection of dye ink images, laminating a recorded surface with a transparent film, etc. to form a protective layer has been proposed for improving water resistance or gloss. Cold lamination with a film that adheres at room temperature, hot lamination using heat to apply the lamination, and the like techniques are proposed. However, these lamination techniques have the following disadvantages. The film tends to wrinkle or entrap air bubbles upon lamination. Because the smoothness of the protective layer is easily affected by the smoothness of the recorded surface, the lamination fails to form a highly smooth protective layer on a porous ink receiving layer having a pigment ink image thereon, resulting in unsatisfactory gloss because of occurrence of gloss unevenness or the like. Considering that it is desirable for a protective layer to have as small a thickness as possible for assuring a satisfactory feeling or texture, thickness reduction achievable by these lamination techniques are limited.
Liquid lamination is also known as a lamination technique, in which a liquid film-forming composition is applied to a recorded surface and dried to form a protective film. Applied to a porous ink receiving layer, however, the film-forming composition will entrap a large number of air bubbles generated from the porous ink receiving layer, only to form a bubble-containing protective layer. Additionally, the liquid lamination is costly because of involvement of a drying step and has difficulty in forming a thin protective film because of difficulty in controlling the film thickness with a reduced amount of the coating composition.
Spray coating formulations are commercially available as a handy means for protecting a recorded image, which comprise a film-forming resin dissolved, together with an aerosolized gas, in an oil-soluble organic solvent, e.g., toluene or xylene. It is difficult to uniformly apply a coating by spraying to form a flat, thin and neat protective film. Moreover, use of the oil-soluble organic solvent is problematical for safety.
Although pigment inks that are superior to dye inks in light fastness or water fastness have been extending their use, the above-mentioned problems peculiar to pigment inks, such as poor scratch resistance and gloss unevenness, still remain unsolved. Ink jet recorded matter possessing both high image quality comparable to silver salt photographs and satisfactory image fastness (long-term storage stability) has not yet been provided.
While a number of methods for laminating an image formed mainly of dye inks with a protective layer have been proposed, there is no laminating method which is capable of improving image gloss and fastness without impairing the original texture or feeling of recorded matter.